Short Messaging Service (SMS) was introduced in 1985 into the 3GPP GSM series of standards for sending messages of up to 160 characters (including spaces) to and from GSM mobile handsets. The initial idea behind SMS was to use a telephony-optimized system, such as GSM, to transport messages on the signalling paths used to control the telephony traffic during time periods when no signalling traffic existed. What was not predicted was the massive shift in social behaviour in following years. Instant Messaging (IM) on PCs shifted a younger generation away from voice calls to text-based communications with its own specialized vocabulary. Later, SMS was adopted for enterprises, content delivery, and entertainment services involving SMS, e.g., TV voting. Using SMS in combination with various location-based services (LBS) applications, such as location-based mobile advertising, has been used in the wireless market, e.g., for delivering discounts to mobile subscribers near advertised restaurants or cinemas. Location information has also been used by emergency call routing entities to route an emergency call to the appropriate (Public Safety Answering Point) PSAP with the minimum delay.
Enhanced Messaging Service (EMS) is based upon standard SMS, but with formatting added to the text. The formatting permits the message to contain animations, pictures, melodies, formatted text, vCard, vCalendar, and Wireless Vector Graphics objects. Such objects may be mixed together into one message.
In the 3GPP standards, SMS is a service described for Public Land Mobile Networks (PLMN) which transfers short messages between a GSM/UMTS mobile station (MS)/user equipment (UE) and a Short Message Entity (SME) via a Service Centre (SC). An SME is an entity which may send or receive Short Messages. The SC normally serves as an interworking and relaying function of the message transfer between the MS and the SME. The SMS service also supports the interchange of short messages between the MS and email servers, which involves Email-to-SMS gateways.
3GPP technical specification TS 23.040 specifies point-to-point and cell broadcast SMS services. The cell broadcast (specified in 3GPP technical specification TS 23.041) is a technology that allows a text or binary message to be defined and distributed to all mobile terminals connected to a set of cells. Cell Broadcast Entities (CBEs) are connected to the Cell Broadcast Centre (CBC). Cell Broadcast messages are then sent from the CBCs to the cells in accordance with the CBC's coverage requirements. Advanced infrastructures make use of Geographic Information System (GIS)-based interfaces for definition of the used areas.
The SMS normally comprises 8 elements particular to the submission and reception of messages:                Validity Period (indicates the time period for which the short message is valid, i.e. for how long the SC shall guarantee its existence in the SC memory before delivery to the recipient has been carried out);        Service Centre Time Stamp (the time of arrival of the short message at SC);        Protocol Identifier (either a reference to the higher layer protocol being used, or interworking with a certain type of telematic device);        More Messages to Send (true when there is one or more messages waiting in that SC);        Priority (information element provided by an SC or SME to indicate to the PLMN whether or not a message is a priority message; Delivery of a priority message shall be attempted irrespective of whether or not the MS has been identified as temporarily absent, or having no free memory capacity);        Messages Waiting (in case of previous unsuccessful delivery attempt(s) due to temporarily absent mobile or MS memory capacity exceeded, the service element enables the PLMN to provide the HLR, SGSN and VLR with which the recipient MS is associated with the information that there is a message in the originating SC waiting to be delivered to the MS);        Alert SC (the service element, which may be provided by some GSM/UMTS PLMNs to inform the SC that an MS is again ready to receive one or more short messages so that the SC may—on reception of an Alert SC—initiate the delivery attempt procedure for the queued messages destined for this MS); and        MT Correlation ID (service element used to verify from where the message is received originated; used only when the HPLMN of the receiving MS is using an SMS Router or an IP-SM-GW).        
SMS may be implemented in different systems and be based on different technologies, such as SMS over IP or SMS over Service Gateways (SGs).
3GPP is in the process of studying a long-term approach to address the need for non-voice emergency services, but it may be several years before this long-term approach is available in the market place. This time frame does not solve the more immediate needs for people with disabilities. There are approaches for SMS to 911 communications targeting near-term intermediate approaches. But they are primarily focused on the upgrades to support interactions on the PSAP side of the communications interface and do not address the end-user devices, the originating wireless networks, and ultimately the SMS shortcomings and limitations (e.g. security, latency, routing etc.).
One of such possible alternatives to these near-term SMS to 911 approaches is to use Terminal Type (TTY) communications with the PSAP without requiring users to attach a separate TTY terminal to their mobile devices. This alternative is commonly called “TTY Emulation”. TTY Emulation establishes a standard circuit-switched emergency voice call, and uses the media path to transmit and receive characters as TTY tones (typically Baudot tones). TTY emulation re-uses emergency voice services, including high reliability, low latency, priority handling and other features. However, one of the recognized challenges with the TTI emulation approach is that generally it is more reliable to transmit and receive signalling between the mobile and base station instead of audible tones.
Another approach is to place a voice call to 911, so that PSAP call taker can identify the caller as one who cannot use speech and is registered for SMS; then the PSAP call taker initiate an SMS text message to that caller. Since the SMS is delivered over the associated control channel that exists as part of the voice call, this eliminates some of the limitations with SMS as the MSC does not have to perform the “paging” process to deliver the SMS. In addition, since there is a voice call established, the normal routing and location capabilities of the voice call are available, eliminating some of the other limitations with SMS. Some disadvantages of this approach, are the inherited SMS “store and forward” nature and the requirement that the user is able to read and send an SMS while on a voice call which is inconvenient and not always possible.
Another approach is real time text where the text is transmitted character by character as the user types the message. Real time text provides a functionality which is not possible with store-and-forward SMS systems enabling conversations equivalent to voice conversations, so that the conversation can be followed closely and that immediate interaction takes place. Real time text requires an IP data connection, as the messages are transported over IP protocols. Capabilities such as automatic routing and location are not defined.
Publication, WO2009021556 (A1), discloses yet another approach. According to this approach emergency information is added as a postfix to the emergency call number. The emergency information may comprise; position indication, ability to voice answer, indication of accompanying SMS, automated alarm etc. and is added as postfix to the emergency number by the phone. The network entry node takes care of separation of dialled emergency number and emergency information, to enable normal set-up of the emergency call connection trough the network to the emergency centre where the emergency information is presented to the emergency operator.
The following describes some of the problems with known approaches. First, there are no network-based messaging-based emergency services in deployed or standardized cellular networks. Emergency positioning (e.g., positioning for E-911 calls in North America or 112 in Europe) is a regulatory requirement in the US. Emergency positioning is typically triggered by setup of an emergency call, i.e., someone dialling the emergency number (911 in the example) on a cell phone. A voice communication between the user and the Public Safety Answering Point (PSAP) is then setup. Such an emergency service may not be feasible for example for people with speech disabilities. Furthermore, there could also be a problem in cases where the 911 call is placed because of a user of the cell phone is being under threat and voice communication with PSAP clients/agents is not possible. Such situations may in fact prevent users from dialling 911 to get assistance, e.g., by the Police. In addition, emergency numbers may also be busy due to a capacity limit, e.g., in a mass disaster situation, and the network capacity is much smaller for voice calls than for messaging services.
Other problems with prior art is that there is no possibility to guarantee caller's identification and delivery. First, it is e.g. possible to spoof SMS messages and make them appear to come from other people's mobile devices. Secondly, SMS is a best-effort service i.e. is it possible to guarantee the delivery and obtain any indication from PSAP about the received or read SMS.
Another problem with prior art solutions is that, no solution provides a possibility to ensure that all messages from a sequence of SMS messages, fragmented or not, within the same emergency session are routed to the same PSAP. Neither the mobile device nor the network has any association between two SMSs sent from the same mobile device, since SMS is a discrete message. As it is now, SMSs may be routed to a different PSAP if the subscriber moves to another location.